Week 8 (Sep 23 - Sep 27)

Monday

As per described on Week 7 (Sep 17 - Sep 20) Tuesday's list of activities, the PDMS was finally put into some molds and left to cure wrapped in aluminum foil at 70°C overnight. Only 5 molds were filled to test for shape and ease of retrieval. They will be retrieved on Tuesday morning. An updated version of the activities list is shown below.

Activities for the week
  • Retrieve and check PDMS cylinders
  • Fill the rest of the molds and cure PDMS
  • Cut PMMA if cylinders don't fit the current bottom layers
  • Fabricate new device and test for fitting and leakages

Furthermore, if there is enough time throughout the week, some additional yet important tasks could be done.

Additional tasks
  • Perform chemical modifications on PDMS cylinder substrates (triplicates yet again)
  • Check modification retainence on the surface before and after insertion in bottom layer

Tuesday

New bottom layers were cut and PDMS molds were filled and left to cure overnight. It is expected that the molds will help the PDMS maintain a good shape for the substrate to completely seal the air chamber and prevent any leakages.

Wednesday

The PDMS substrates were retrieved. Upon 3 tests, the best way to remove them is to separate the piece from the walls of the cylinder mold using pointy tweezers. Then, when most of it has separated, push the substrate out.
The device was successfully fabricated. The PDMS substrate was slightly bigger than the hole, so there is some effort required to fit it inside the device. However, it can be done in a way that most of the surface remains untouched during the process, which will be further confirmed with modification experiments.
First, an issue must be addressed: the thickness of the middle layer, which gives height to the middle layer, is very small. With the insertion of the PDMS substrate, the surface ends up touching the internal face of the top layer, which can potentially damage the surface modification.

Successes
  • Fabricated PDMS cylinders that fit into the holes
  • No leakages were found in the device
  • Reciprocation was achieved
Issues found
  • Due to the insertion procedure of the PDMS substrate, surface touches the top layer. Modifications might get damaged
Solution of issues
  • Middle layer of 1mm and holes on bottom layer closer to entrance can lead to better performance with the same sample volume

Flow reciprocation was achieved. To test for both leakages and reciprocation, the device was spun. If no sign of leakage was perceptible, the device was stopped and the recession of the fluid was observed.
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